Summary
Using base64 encoding for text content instead of UTF-8 or quoted-printable negatively impacts email deliverability. Base64 increases message size, can trigger spam filters due to historical association with spam, and is generally inappropriate for text. Quoted-printable is preferred for text due to readability and smaller size. Proper email setup (SPF, DKIM, DMARC), clean HTML coding, good sender reputation, and avoiding spam trigger words are crucial. Character set encoding (especially UTF-8 and non-ASCII) needs correct implementation.
Key findings
- Encoding Impact: Base64 negatively impacts deliverability when used for text.
- Spam Triggers: Excessive/inappropriate encoding triggers spam filters.
- Message Size: Base64 increases message size.
- Encoding Alternatives: Quoted-printable is preferred for text; UTF-8 requires proper handling.
- Authentication: SPF, DKIM, DMARC are essential for authentication and deliverability.
- HTML & Content: Clean HTML, no spam trigger words, and sender reputation are vital.
Key considerations
- Choose Encoding Wisely: Use quoted-printable for text, base64 only for binary.
- Minimize Message Size: Avoid unnecessary bloat from base64 encoding.
- Implement Authentication: Set up SPF, DKIM, and DMARC to improve trust.
- Clean HTML: Ensure clean, well-formatted HTML to avoid spam triggers.
- Monitor Reputation: Maintain a good sender reputation.
- Test Emails: Test emails across clients to ensure proper rendering and avoid spam filters.
- Character Sets: Correctly encode character sets, particularly non-ASCII characters and UTF-8.
What email marketers say
9 marketer opinions
Using base64 encoding for text content instead of UTF-8 can negatively impact email deliverability. Base64 increases message size, potentially causing rejection by servers or impacting sender reputation. Excessive or unnecessary encoding can trigger spam filters, as it appears suspicious. Proper email setup (SPF, DKIM, DMARC) and clean HTML coding are crucial for deliverability. Maintaining a good sender reputation and avoiding spam trigger words also play a significant role.
Key opinions
- Message Size: Base64 encoding increases message size, which can lead to deliverability issues.
- Spam Filters: Excessive encoding can trigger spam filters.
- Authentication: Proper email authentication (SPF, DKIM, DMARC) is essential for deliverability.
- HTML Coding: Clean and well-formatted HTML is preferable for deliverability.
- Sender Reputation: A good sender reputation is crucial for emails to reach the inbox.
- Spam Trigger Words: Using spam trigger words can negatively impact deliverability.
Key considerations
- Encoding Choice: Prefer UTF-8 for text content and avoid unnecessary base64 encoding.
- Email Size: Keep email size to a minimum to avoid rejection by servers.
- HTML Structure: Use clean and simple HTML structures.
- Authentication Setup: Implement SPF, DKIM, and DMARC for email authentication.
- Sender Reputation Management: Maintain a good sender reputation by warming up IP addresses, cleaning up contact lists, and avoiding spam traps.
- Content Optimization: Avoid spam trigger words and test email rendering across different clients.
Marketer view
Email marketer from Sendinblue recommends keeping HTML email designs simple and using inline CSS for better compatibility across email clients. Avoid complex or unusual HTML structures, which could inadvertently trigger spam filters. Clean, well-formatted HTML is preferable for deliverability.
7 Dec 2022 - Sendinblue
Marketer view
Email marketer from Reddit shares that excessively encoding an email message may make it appear suspicious. Suggests that it can trigger spam filters if the encoding is seen as an attempt to hide the content.
21 Jul 2022 - Reddit
What the experts say
6 expert opinions
Experts agree that using base64 encoding for text instead of quoted-printable or UTF-8 negatively impacts email deliverability. Base64's historical association with spam and its inappropriateness for text-based content raise red flags for spam filters. Quoted-printable is recommended for text, especially non-ASCII, due to better readability and smaller size. Proper character set declaration is also crucial. The choice between quoted-printable and base64 should be based on content type, with base64 reserved for binary data.
Key opinions
- Historical Spam Association: Base64 encoding was previously used by spammers, leading to negative reputation.
- Encoding Appropriateness: Base64 is less suitable for text content than quoted-printable or UTF-8.
- Readability and Size: Quoted-printable offers better readability and smaller size for text-based emails.
- Spam Filter Triggers: Encoding content unnecessarily can trigger spam filters.
- Character Set: Properly declaring the character set is essential for accurate display.
Key considerations
- Content Type: Choose encoding based on content type: quoted-printable for text, base64 for binary.
- Encoding Best Practices: Avoid base64 encoding of text; use quoted-printable unless there's a specific need for base64.
- Spam Filter Avoidance: Refrain from unnecessary encoding to prevent triggering spam filters.
- Character Set Declaration: Ensure proper character set declaration (e.g., UTF-8) for accurate text display.
- Human Review: Consider human review: quoted-printable allows easier content inspection.
Expert view
Expert from Spam Resource shares that email filters look at a variety of things but in general if you are encoding things that should not be encoded that it will likely be flagged negatively by spam filters. If you base64 encode text that should not be encoded you will negatively impact your deliverability.
2 Dec 2023 - Spam Resource
Expert view
Expert from Email Geeks explains that there was a time when base64 encoding plain text was assigned negative reputation due to spammers using it to bypass early content filters. Filters started cracking the Base64 encoding. Recommends Quoted Printable encoding if high ASCII is needed.
6 Aug 2021 - Email Geeks
What the documentation says
5 technical articles
Technical documentation emphasizes the importance of using appropriate content transfer and character encodings for email deliverability. Base64 and quoted-printable serve different purposes: base64 for binary data and quoted-printable for text. Proper character set encoding, especially for non-ASCII characters, is critical to avoid display issues and spam filters. UTF-8 is a widely supported character encoding, but it requires correct implementation. Furthermore, email authentication (SPF, DKIM, DMARC) is crucial for establishing trust and preventing emails from being marked as spam, particularly for Gmail users.
Key findings
- Encoding Purpose: Base64 is for binary data, quoted-printable for text.
- Character Set Encoding: Proper encoding of character sets (especially non-ASCII) is crucial.
- UTF-8 Importance: UTF-8 is dominant but requires correct implementation.
- Display Issues: Incorrect encoding can cause display issues (mojibake) that affect deliverability.
- Email Authentication: SPF, DKIM, and DMARC are crucial for deliverability, especially for Gmail.
Key considerations
- Encoding Choice: Select content transfer encoding based on data type (binary vs. text).
- Character Set Implementation: Implement character set encoding correctly, following RFC 2047 guidelines for headers.
- UTF-8 Handling: Ensure proper handling of UTF-8 encoding to prevent display errors.
- Authentication Setup: Set up SPF, DKIM, and DMARC to authenticate emails and improve deliverability.
- Email Testing: Test emails to ensure correct rendering and avoid spam filters.
Technical article
Documentation from Google shares that authenticating your email with SPF, DKIM, and DMARC is crucial for deliverability to Gmail users. A strong authentication setup improves trust and prevents your emails from being marked as spam. Ensure your domain meets Google's email authentication standards.
8 Aug 2022 - Google
Technical article
Documentation from MDN explains that UTF-8 is a dominant character encoding for the web and email. Using UTF-8 ensures broad compatibility and correct display of text across different systems. Improper handling of UTF-8 can lead to garbled text, which might affect deliverability if it makes the email appear unprofessional or suspicious.
22 Dec 2022 - Mozilla Developer Network
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